Metal parts having precise dimensional tolerances can be made of titanium or titanium alloys are conventionally made by casting, forging or machining from a billet. These techniques can require large lead times or high material use of the expensive titanium metal, or both, in the fabrication of the metal part.
Fully dense physical objects may be made by a manufacturing technology known as rapid prototyping, rapid manufacturing, layered manufacturing, solid freeform fabrication (SFFF), additive fabrication, additive manufacturing and 3D printing. This technique employs computer aided design (CAD) software to first construct a virtual model of the object which is to be made, and then transform the virtual model into thin parallel slices or layers, usually horizontally oriented. The physical object can then be made by laying down successive layers of raw material in the form of liquid, paste, powder or other layerable, spreadable or fluid form, such as melted metal, e.g., from a melted welding wire, or preformed as sheet material resembling the shape of the virtual layers until the entire object is formed. The layers can be fused together to form a solid dense object.
Solid freeform fabrication is a flexible layered manufacturing technique allowing creation of objects of almost any shape at relatively fast production rates, typically varying from some minutes to several days for each object. The technique is thus suited for formation of prototypes and small production series, and can be scaled up for mass production.
The technique of layered manufacturing can be expanded to include deposition of pieces of the construction material, that is, each structural layer of the virtual model of the object is divided into a set of pieces which when laid side by side form the layer. This allows forming metallic objects by welding a wire onto a substrate in successive stripes forming each layer according to the virtual layered model of the object, and repeating the process for each layer until the entire physical object is formed. The accuracy of the welding technique is usually too coarse to allow directly forming the object with acceptable dimensions. The formed object will thus usually be considered a green object or pre-form which needs to be machined to acceptable dimensional accuracy.
Taminger and Hafley (“Electron Beam Freeform Fabrication for Cost Effective Near-Net Shape Manufacturing”, NATO/RTOAVT-139 Specialists' Meeting on Cost Effective Manufacture via Net Shape Processing (Amsterdam, the Netherlands, 2006) (NATO)) discloses a method and device for manufacturing structural metal parts directly from computer aided design data combined with electron beam freeform fabrication (EBF). The structural part is built by welding on successive layers of a metallic welding wire which is welded by the heat energy provided by the electron beam. The EBF process involves melting a metal wire into a molten pool made and sustained by a focused electron beam in a high vacuum environment. The positioning of the electron beam and welding wire is obtained by having the electron beam gun and the actuator supporting the substrate movably hinged along one or more axis (X, Y, Z, and rotation) and regulate the position of the electron beam gun and the support substrate by a four axis motion control system. The process is reported to be nearly 100% efficient in material use and 95% effective in power usage. The method can be employed both for bulk metal deposition and finer detailed depositions, and the method is claimed to obtain significant effect on lead time reduction and lower material and machining costs as compared to the conventional approach of machining the metal parts. The electron beam technology has a disadvantage of being dependent upon a high vacuum of 10−1 Pa or less in the deposition chamber.
It is known (e.g., see Adams, U.S. Pat. Pub. No. 2010/0193480) to use a TIG-welding torch to build objects by SFFF, where successive layers of metallic feedstock material with low ductility are applied onto a substrate. A plasma stream is created by energizing a flowing gas using an arc electrode, the arc electrode having a variable magnitude current supplied thereto. The plasma stream is directed to a predetermined targeted region to preheat the predetermined targeted region prior to deposition. The current is adjusted and the feedstock material is introduced into the plasma stream to deposit molten feedstock in the predetermined targeted region. The current is adjusted and the molten feedstock is slowly cooled at an elevated temperature, typically above the brittle-to-ductile transition temperature of the feedstock material, in a cooling phase to minimize the occurrence of material stresses.
Withers et al. (U.S. Pat. Pub. No. 2006/185473) also describes using a TIG torch in place of the expensive laser traditionally used in a solid freeform fabrication (SFFF) process with relatively low cost titanium feed material by combining the titanium feed and alloying components in a way that considerably reduces the cost of the raw materials. Withers et al. also describes using titanium sponge material mixed with alloying elements formed into a wire where it can be used in an SFFF process in combination with a plasma welding torch or other high power energy beams to produce near net shaped titanium components.
Abbott et al. (WO 2006/133034, 2006) describes a direct metal deposition process using a laser/arc hybrid process to manufacture complex three-dimensional shapes comprising the steps of providing a substrate and depositing a first molten metal layer on the substrate from a metal feedstock using laser radiation and an electric arc. The electric arc in gas metal arc welding can be provided by using the metal feedstock as an electrode. Abbott et al. teaches that the use of laser radiation in combination with gas metal arc welding stabilizes the arc and purportedly provides higher deposition rates. Abbott et al. utilizes a consumable electrode guided by and exiting out of a wire guide. The metal of the consumable electrode is melted at the end and the molten metal is deposited by positioning the end over the deposition point. The required heat for melting the consumable electrode is supplied by an electric arc expanding between the tip of the electrode and the workpiece/deposition substrate, and by a laser irradiating the deposition area. Welding by melting a consumable electrode heated by an electric arc is known as gas metal arc welding (GMAW), of which in the case of using non-reactive gases to make the arc is also denoted as metal inert gas welding (MIG-welding).
Titanium metal or titanium alloys heated above 400° C. may be subject to oxidation upon contact with oxygen. It is thus necessary to protect the weld and heated object which is being formed by layered manufacture against oxygen in the ambient atmosphere. WO 2009/068843 discloses an inert gas shield for welding which produces an even outflow of protecting inert gas. By placing the shield above the object which needs to be protected, the even flow of inert gas will displace ambient atmosphere without creating vortexes which may entrain ambient oxygen containing gas. The shield can be formed as a hollow box of which the inert gas enters the interior and is allowed to escape the interior of the box through a set of narrow openings made in one wall of the box. Another solution to preventing oxidation of the titanium is to conduct the deposition process under vacuum.
For the above processes, the apparatus used often involves a single chamber that is required to be evacuated or in which the atmosphere must be replaced every time it is loaded or unloaded and before the deposition can begin. Similar types of single chamber apparatuses are also used in coating and heating processes. Some examples include those disclosed in U.S. Pat. No. 4,328,257 disclosing a single chamber apparatus used for plasma coating. U.S. Patent Application Publication No. 2005/0173380 discloses a single vacuum chamber equipped with an electron beam gun used to accomplish the deposition. U.S. Patent Application Publication No. 2002/0139780 discloses a single chamber apparatus used for welding deposition.
A problem to be addressed is the speed of the deposition process and the expenses resulting from the evacuation the chamber every time a new substrate is loaded or unloaded. Also, during plasma arc deposition, it is important to be able to control the temperature of chamber and of the equipment to prevent overheating. The temperature control must be achieved while still preventing the titanium metal or titanium alloys being heated above 400° C. from being subject to oxidation by preventing contact with oxygen.
There exists a need, therefore, for a chamber deposition system that provides a more efficient and cost effective process that addresses one or more of the above problems. This can further lead to increased throughput and yield of direct metal deposition formed products without the risk of oxidation.